A motor has been structured by various methods, and one of the conventional methods is this: A rotor and a stator are combined together such that a magnetic center of the rotor is away from a magnetic center of the stator by a given distance relative to an axial direction of a shaft. In this case, the rotor is supported by using the force to bring the magnetic center of the rotor in agreement with that of the stator along the axial direction. When a device including the foregoing motor is mounted to, e.g. a vehicle, a difference can be generated in a gravity-working direction acting on the motor depending on the mounted status of the device. If the difference is generated in the gravity-working direction, the motor structure discussed above allows no change in positional relation between the rotor and the stator along the axial direction, whereby a steady motor function is obtainable.
On the other hand, when the vehicle runs on a bad road, a strong shock is applied to the foregoing on-vehicle motor, then the rotor jumps and hits a bearing, thereby producing a collision sound. Techniques for overcoming this problem, i.e. lowering the collision sound, have been proposed, e.g. refer to Patent Literature 1. One of these techniques proposes that a round groove and a dumper ring are provided on the outer wall near the shaft end.
A conventional dumper ring should be mounted to the shaft properly, so that the motor structure becomes complicated, which requires complex assembling work and thus lowers an efficiency of the assembly. On top of that, use of the dumper ring increases the number of components.
Patent Literature: Unexamined Japanese Patent Application Publication No. 2009-254193